This invention relates to an audio apparatus such as a radio or the like mounted on a vehicle such as a motorcar, a motorcycle, or the like.
The use of such an audio apparatus mounted on a vehicle becomes increasingly difficult with the increase in speed due to driving noises. Because driving noises, which are partially composed of wind noise, increase as the vehicle speed increases the sound volume of an audio apparatus previously set, at the time of a lower vehicle speed is overcome by the driving noises, if the sound volume adjusting knob of the audio apparatus is not adjusted. Accordingly, the sound volume is increased by adjusting the volume knob of the audio apparatus by the operator, but this is inconvenient because the manual adjustment must be made every time the vehicle speed is changed.
In addition, in a previously known apparatus, noise in a vehicle is detected and the volume of the audio apparatus is automatically increased or decreased according to the amount of detected noise. This type of apparatus, however, is inconvenient because it is complex in construction and high in price. It requires a microphone for detecting the amount of noise and a filter circuit for discriminating between noise and sound emitted from the